Survival analysis is the method used to study the impact of treatment on outcome, when outcome is defined as the time elapsed prior to an event. This procedure has wide application in the field of mental health research as well as other fields. The goal of this project is to develop a computer program that researchers can used to find the appropriate sample size for a planned study that will employ survival analysis. The program will be developed as an update to a power analysis program that was developed under an earlier SIR grant and is currently being distributed by SASS, and will expand on the current program in four ways. (1) It will incorporate the ability to perform power analysis for a wide variety of survival procedures. (2) It will allow users to find the sample size to test specific alternate hypotheses as well as the null hypothesis of no effect. (3) It will allow users to take into account the width of the confidence interval as well as the statistical power. (4) It will allow the user to test for the equivalence of treatments. PROPOSED COMMERCIAL APPLICATION: The project will produce a micro-computer program that computes statistical power and precision for studies that employ survival analysis. The program will have wide application in the fields of mental health research and medical research as well as the social sciences. The program will be marketed by SASS and LEA, which have marketed our earlier programs.